Mechanical actions and chemical reactions both help to create and stabilize foam in papermaking and effluent systems, particularly where elevated temperatures are concerned. In the papermaking process, inadequate foam control can cause loss of production through reduced machine speeds, caused by diminished drainage and reduced drying efficiency, as well as lower product quality caused by poor sheet formation. The efficiency of effluent systems is greatly reduced when control of foam in the system is lost.
It is widely known that foam is a colloidal system in which a gas is dispersed in a liquid. This foam can exist as bubbles of gas entrained in the bulk of the liquid medium or as a combination of entrained gas and visual foam on the surface of the liquid. Both the surface foam and trained gas contribute to reducing production efficiency.
The pumping of liquids through pipes, strainers, refiners and other types of processing equipment can create foam mechanically. Foam can be stabilized by salts of rosin acids, fatty acids, and lignins that absorb at the air/liquid interface. Finely divided particles such as starch, cellulose, and fillers also contribute to the stabilization of foam. Defoamers are added to the foaming medium in order to prevent foam formation or cause collapse of existing foam. The collapse of the foam is accomplished by dewetting the surface by a hydrophobic particle which enters the air/ liquid interface in the lamella of the bubble. Due to capillary forces, the lamella drains sufficiently on both sides, causing a weak point or hole in the film, which leads to rupture of the lamella.
Most conventional defoamers are comprised of a hydrophobic material such as a saturated long chain fatty acid or fatty alcohol having a melting point greater than about 105.degree. F., or an insoluble hydrophobically modified particle, such as silica dispersed in an oil phase. These products generally use hydrocarbon oil as a carrier and can be diluted with water. Some products can be produced as 100% water-based emulsions. These compositions generally require extensive processing such as heating, cooling, and homogenization. These compositions also tend to quickly become unstable over short periods of time.
Conventional defoamer/antifoam compositions include ethylene (bis) stearamide (EBS), fatty alcohol, fatty acid or hydrophobic silica. Problems result from the use of these products because they are particulate and will aggravate deposition. Additionally, some defoamer/antifoam products may include a hydrocarbon oil carrier. Such products are known to negatively effect paper sheet properties, such as brightness and sizing.
These and other problems associated with the use of conventional defoamer/antifoams in the wet end of a papermaking operation, which is basically the fiber slurry (commonly known as white water) from which the sheet of paper is made, are resolved by the present invention.
It is an object of the present invention to provide an improved foam control composition for elevated temperatures in the pulp and papermaking process. It is a further object of the present invention to eliminate the necessity of heating, cooling and/or homogenizing with respect to processing. It is also an object of the present invention to produce a stable foam control composition. The foam control composition comprises a polyether surfactant and a polyethoxylated sorbitol hexaoleate. This composition is a concentrated, dispersible product containing no hydrocarbon oil, water or particulate and can be processed by blending at ambient temperatures. The combination of ingredients of the present invention produces a composition which is stable at least for three months at storage temperatures ranging from 40.degree. F. to 140.degree. F. The foam control composition is added to aqueous systems but is particularly effective in controlling foam generated in papermaking operations at elevated temperatures of 120.degree. F. and above.